Ionic, Covalent, and Metallic Bonding

Compound A compound is a substance that contains two or more different elements chemically combined.

Three Types of Bonds Ionic Covalent Metallic

Basics of Chemical Bonding Bond formation is an exothermic process, which means energy is released. This results in a lower, more stable energy state. Bonding is done by the valence electrons. The purpose of bonding is so atoms have full valence shells, or that they satisfy the octet rule. Octet Rule: Tendency of valence electrons to arrange themselves during chemical reactions so each atom has a stable octet (8 electrons) in the valence shell. When the atom has a full valence shell, it is most stable. Exception: Hydrogen’s stable arrangement is 2 electrons in the valence shell. He, Be, and B will also have a stable arrangement of 2 electrons.

Ionic Bonds What is an ionic bond? An ionic bond is a bond formed by the electrostatic attraction between cations and anions (positive ions and negative ions attract). A compound composed of cations and anions is called an ionic compound. Electrostatic attraction/force – attraction between positive and negative charges.

Ionic Bonds Ionic bonds are generally between metals and nonmetals Ionic bonds are generally formed between one or more elements in which there is a large difference in electronegativity (>1.7) Most ionic compounds are solid at room temperature Ionic compounds form crystal lattices, a continuous array of ions

Ionic Bonds NaCl, or table salt, crystal lattice

Ionic Bonds The chemical formula for an ionic compound is called a formula unit. It is the lowest whole number ratio of ions in an ionic compound. Ex: Sodium Chloride: For every one Na+ ion, there is one Cl- ion, or a 1:1 ratio. So NaCl represents a formula unit of sodium chloride.

How Ionic Bonds are Formed Atom of metal and nonmetal come in close contact Metal loses electron(s) to the nonmetal. Nonmetal takes the electron(s) from the metal, forming a cation and anion Electrostatic force of attraction between positively charged cation and negatively charged anion hold atoms together

How Ionic Compounds Form

Covalent Bonds A covalent bond is a bond formed in which atoms are held together by sharing electrons. A neutral group of atoms joined together by covalent bonds is called a molecule.

Covalent Bonds Covalent bonds are generally between two nonmetals Covalent bonds are generally formed between one or more elements in which there is a small or no difference in electronegativity Most molecular compounds are liquids or gases at room temperature A molecular compound is a compound made of molecules.

Covalent Bonds A molecular formula is the chemical formula of a covalent compound. A molecular formula tells the actual number of atoms in each molecule. Ex: water: A water molecule is made of two hydrogen atoms and one oxygen atom, so the molecular formula is H2O.

How Covalent Bonds are Formed Atoms of two nonmetals come in close contact Electrons of atoms are attracted to the nucleus of the other atom Orbitals overlap and electrons are shared forming single, double, or triple bonds

How Covalent Bonds are Formed

Ionic vs. Covalent Bonds Ionic compound – salt Made of crystal lattice, or array of ions Formula unit: NaCl Chemical formula: NaCl Molecular compound – water Made of water molecules Molecule: H2O Chemical formula: H2O

Metallic Bonds Metallic bonds: Bonds between two or more metal atoms. Ex: Copper wire, coins, steel Metallic bonding: The electron sea model

Metallic Bonds Explained Metal-Metal bond Valence electrons are mobile (delocalized) and move freely between metal ions Crystal lattice array of positive ions immersed in an electron sea. Held together by an electrostatic force between metal ions and the sea of electrons.

Crystal Lattice Examples

The Electron Sea Explains Metal Characteristics Conductivity Electricity: Flow of electrons Since valence electrons are free moving, metals conduct electricity easily Malleability and Ductility The electrons insulate the metal cations from one another. If put under pressure, metal cations can slide past each other like ball bearings in oil.

Alloys An alloy is a homogeneous mixture of metals. Made by melting and resolidifying. Often, properties of alloys are superior to the individual metals. Examples Steel: Iron, chromium, carbon Sterling silver: Silver, copper Brass: Copper, zinc Bronze: Copper, tin